Development of an Aptamer/CRISPR-Cas12a-Based Dual-Modal Biosensor for <i>Fusobacterium nucleatum</i> Detection in Non-Invasive Colorectal Cancer Screening

Colorectal cancer (CRC) is the third most common cancer and leading cause of cancer-related deaths worldwide. However, current CRC screening methods are complex, invasive, and tend to exhibit low sensitivity. Recent evidence has highlighted gut microbiota dysbiosis, especially elevated <i>Fusobacterium nucleatum</i> levels, as a promising biomarker for CRC. In this study, a sensitive and specific detection platform was developed for <i>F. nucleatum</i> by combining a highly specific aptamer with rolling circle amplification (RCA) and the CRISPR/Cas12a technology. The aptamer enables specific target recognition, while RCA amplifies the target signal, and the Cas12a-mediated cleavage of a fluorescence-quenching substrate generates a quantifiable fluorescence or grayscale signal. Using a microplate reader, this assay achieved a limit of detection (LOD) of 3.68 CFU/mL; furthermore, by incorporating smartphone-assisted ImageJ grayscale analysis, it elevated the LOD to 4.30 CFU/mL, thereby enabling a dual-mode output along with on-site applicability. Additionally, the strong correlation between the two signals allowed for mutual validation. Upon application to clinical fecal samples, the developed method sensitively distinguished CRC patients from healthy controls, and its results correlated with the quantitative polymerase chain reaction results. This triple-synergistic platform, integrating aptamer specificity, RCA amplification, and CRISPR/Cas12a sensitivity, enables the noninvasive, ultrasensitive detection of <i>F. nucleatum</i>, supporting early CRC screening, prognosis monitoring, and microbiome-targeted therapy. Moreover, this approach overcomes the challenges of detecting low-abundance bacteria in early stage CRC and advances the precision of microbiome-based diagnostics for CRC.